1. Field of the Invention
The present invention relates to a flat panel display and a semiconductor device for use therein, and more particularly, to a flat panel display having a drive circuit mounted thereon and a semiconductor device for use therein.
2. Description of the Background Art
Recently, plasma display panels (hereinafter also referred to as PDPs) are becoming increasingly common as big-screen flat panel displays not only for business use but also for consumer use. A PDP has front and rear glass substrates joined to each other, and a space therebetween is filled with a discharge gas. The glass substrates filled with a discharge gas is called a display panel. A drive circuit including a power device is mounted on the rear side of the display panel. This power device supplies current to the display panel, so that a desired image is displayed on the display panel.
A PDP requires a drive circuit capable of applying a high voltage of not lower than 300V at the maximum and flowing a current of 200 A for an instant. Such drive circuit includes many circuit portions, and one of them called a sustain circuit requires the highest current capacity. Another portion called an energy recovery circuit also requires a high current capacity.
An X electrode and a Y electrode are formed on the display panel in parallel with each other. Current is applied to these electrodes from the sustain circuit, to generate a discharge between the electrodes. In a surface discharge type AC-PDP, electrodes are covered with a dielectric, and therefore, a capacitive load occurs between the X and Y electrodes. Accordingly, in the sustain circuit, an upper switching element for raising voltage to a level necessary for driving the PDP and a lower switching element for reducing voltage to zero are connected constitute a half-bridge circuit. In an actual PDP, other various switching elements and circuits are also provided such that a plurality of levels of voltage and complicate waveforms can be applied for performing a display operation.
Driving a PDP causes charge/discharge of a capacitive load, at which time a very large current flows, which greatly increases losses of switching elements of a sustain circuit. To prevent this and to effectively utilize an electric charge stored in the capacitive load, an energy recovery circuit is provided. The energy recovery circuit temporarily transfers an electric charge stored in the capacitive load to a capacitor provided in the energy recovery circuit to thereby effectively utilize electric power, and reduces current flowing in the switching elements of the sustain circuit to thereby reduce losses by a large amount.
The sustain circuit and energy recovery circuit are each provided with a plurality of switching elements. Usually, field effect transistors (hereinafter also referred to as FETs) are used for these switching elements. Since a PDP is driven at frequencies ranging approximately from 100 kHz to 250 kHz, an FET capable of performing switching at high speeds needs to be adopted as a switching element.
However, since a large current of about 200 A is necessary for an instant for driving a PDP, one FET is not enough to drive the whole PDP in terms of current capacity. Further, to reduce losses of FETs to a realistic value, a plurality of FETs need to be connected in parallel.
An FET has a great advantage over other switching elements for use in driving a PDP in terms of high-speed switching. However, a plurality of FETs need to be connected in parallel in the drive circuit of a PDP since driving of the PDP requires a very large current as described above. The need for a plurality of FETs creates the need for a large circuit board on which the FETs are mounted and the need for large radiator plates (hereinafter also referred to as radiator fins), which is a problem in achieving size reduction and cost reduction of products.
Therefore, attempts are being made to drive a PDP with a smaller number of switching elements instead of FETs. For instance, Japanese Patent Application Laid-Open No. 2000-330514 proposes using an insulated gate bipolar transistor (hereinafter also referred to as IGBT) for the drive circuit of a PDP. An IGBT has advantages over an FET in larger current capacity, lower ON voltage (ON-state resistance) and little variation in ON voltage even with higher device temperatures. The use of IGBT for the drive circuit of a PDP allows a switching element formed by a plurality of FETs connected in parallel to be replaced by one IGBT. Driving a PDP with one IGBT will substantially reduce the number of switching elements, which can reduce a circuit board in area.
The drive circuit of a flat panel display is provided on the rear plate supporting the display panel. Thus, the flat panel display increases in size as the drive circuit increases in size. Particularly, in the case of using FETs in the drive circuit, large radiator fins are required, which increases the drive circuit in size in the direction of thickness of the flat panel display. Since flat panel displays such as PDPs are characterized by small thickness, such large radiator fins cause a serious problem that interferes with the slimming down of flat panel displays.